This pilot project proposal deals with the identification of epidermal stem cells using an intracellular genetic marker (LacZ). Porcine partial thickness wounds will be created and keratinocytes which are candidates for epidermal stem cells will be transduced with the LacZ gene driven by the CMV promoter. The particle-mediated gene transfer will be used employing a helium driven burst of gold beads which are coated with plasmid DNA containing the LacZ sequence. The LacZ transduced keratinocytes will then be identified with X-gal staining. Serial biopsies will be taken from wounds for up to thirty days, sectioned and stained in order to monitor presence of LacZ gene expression. In order to minimize possible negative effects from trauma, desiccation, heat loss, etc., the wounds will be individually enclosed in vinyl chambers and treated in a placebo fluid containing normal saline and tissue culture concentrations of penicillin and streptomycin. In parallel with the monitoring of the transduced cells, H&E histologies will be used for gross histologic evaluation of the proliferating cells. In the second phase of the project, keratinocytes within wound beds will be transfected using PDGF-A and B plasmids. Expression of PDGF in the wound fluid will be monitored with ELISA. Wound healing will be assessed non-invasively by a protein efflux assay which has been found to reproducibly predict the re-establishment of an epithelial barrier. If the pilot study yields positive results, continued studies will include evaluating the stem cell as a target for somatic cell gene transfer and the influence of genetic manipulation upon its proliferative pattern. It would also open possibilities to study the mechanisms which govern the behavior of the stem cell in the wound repair process.